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Annotation of 41BSD/cmd/px/malloc.c, revision 1.1

1.1     ! root        1: /* Copyright (c) 1979 Regents of the University of California */
        !             2: 
        !             3: static char sccsid[] = "@(#)malloc.c 4.1 10/10/80";
        !             4: 
        !             5: /*
        !             6:  * Patched up version of malloc to do an integrity check
        !             7:  * on each allocation or free.
        !             8:  */
        !             9: 
        !            10: #ifdef debug
        !            11: #define ASSERT(p,t) if(!(p))return(t(TRASHED));else
        !            12: #else
        !            13: #define ASSERT(p,t)
        !            14: #endif
        !            15: 
        !            16: /*     avoid break bug */
        !            17: #ifdef pdp11
        !            18: #define GRANULE 64
        !            19: #else
        !            20: #define GRANULE 0
        !            21: #endif
        !            22: /*     C storage allocator
        !            23:  *     circular first-fit strategy
        !            24:  *     works with noncontiguous, but monotonically linked, arena
        !            25:  *     each block is preceded by a ptr to the (pointer of) 
        !            26:  *     the next following block
        !            27:  *     blocks are exact number of words long 
        !            28:  *     aligned to the data type requirements of ALIGN
        !            29:  *     pointers to blocks must have BUSY bit 0
        !            30:  *     bit in ptr is 1 for busy, 0 for idle
        !            31:  *     gaps in arena are merely noted as busy blocks
        !            32:  *     last block of arena (pointed to by alloct) is empty and
        !            33:  *     has a pointer to first
        !            34:  *     idle blocks are coalesced during space search
        !            35:  *
        !            36:  *     a different implementation may need to redefine
        !            37:  *     ALIGN, NALIGN, BLOCK, BUSY, INT
        !            38:  *     where INT is integer type to which a pointer can be cast
        !            39: */
        !            40: #define INT int
        !            41: #define ALIGN int
        !            42: #define NALIGN 1
        !            43: #define WORD sizeof(union store)
        !            44: #define BLOCK 1024     /* a multiple of WORD*/
        !            45: #define BUSY 1
        !            46: #define NULL 0
        !            47: #define TRASHED -1
        !            48: #define testbusy(p) ((INT)(p)&BUSY)
        !            49: #define setbusy(p) (union store *)((INT)(p)|BUSY)
        !            50: #define clearbusy(p) (union store *)((INT)(p)&~BUSY)
        !            51: 
        !            52: union store { union store *ptr;
        !            53:              ALIGN dummy[NALIGN];
        !            54:              int calloc;       /*calloc clears an array of integers*/
        !            55: };
        !            56: 
        !            57: static union store allocs[2];  /*initial arena*/
        !            58: static union store *allocp;    /*search ptr*/
        !            59: static union store *alloct;    /*arena top*/
        !            60: char   *sbrk();
        !            61: 
        !            62: char *
        !            63: malloc(nbytes)
        !            64: 
        !            65:        unsigned nbytes;
        !            66: {
        !            67:        register union store *p, *q;
        !            68:        register nw;
        !            69:        static temp;    /*coroutines assume no auto*/
        !            70: 
        !            71:        if(allocs[0].ptr==0) {  /*first time*/
        !            72:                allocs[0].ptr = setbusy(&allocs[1]);
        !            73:                allocs[1].ptr = setbusy(&allocs[0]);
        !            74:                alloct = &allocs[1];
        !            75:                allocp = &allocs[0];
        !            76:        }
        !            77:        nw = (nbytes+WORD+WORD-1)/WORD;
        !            78:        ASSERT(allocp>=allocs && allocp<=alloct,(char *));
        !            79:        ASSERT(allock(),(char *));
        !            80:        for(p=allocp; ; ) {
        !            81:                for(temp=0; ; ) {
        !            82:                        if(!testbusy(p->ptr)) {
        !            83:                                while(!testbusy((q=p->ptr)->ptr)) {
        !            84:                                        ASSERT(q>p&&q<alloct,(char *));
        !            85:                                        p->ptr = q->ptr;
        !            86:                                }
        !            87:                                if(q>=p+nw && p+nw>=p)
        !            88:                                        goto found;
        !            89:                        }
        !            90:                        q = p;
        !            91:                        p = clearbusy(p->ptr);
        !            92:                        if(p>q)
        !            93:                                ASSERT(p<=alloct,(char *));
        !            94:                        else if(q!=alloct || p!=allocs) {
        !            95:                                ASSERT(q==alloct&&p==allocs,(char *));
        !            96:                                return(NULL);
        !            97:                        } else if(++temp>1)
        !            98:                                break;
        !            99:                }
        !           100:                temp = ((nw+BLOCK/WORD)/(BLOCK/WORD))*(BLOCK/WORD);
        !           101:                q = (union store *)sbrk(0);
        !           102:                if(q+temp+GRANULE < q) {
        !           103:                        return(NULL);
        !           104:                }
        !           105:                q = (union store *)sbrk(temp*WORD);
        !           106:                if((INT)q == -1) {
        !           107:                        return(NULL);
        !           108:                }
        !           109:                ASSERT(q>alloct,(char *));
        !           110:                alloct->ptr = q;
        !           111:                if(q!=alloct+1)
        !           112:                        alloct->ptr = setbusy(alloct->ptr);
        !           113:                alloct = q->ptr = q+temp-1;
        !           114:                alloct->ptr = setbusy(allocs);
        !           115:        }
        !           116: found:
        !           117:        allocp = p + nw;
        !           118:        ASSERT(allocp<=alloct,(char *));
        !           119:        if(q>allocp) {
        !           120:                allocp->ptr = p->ptr;
        !           121:        }
        !           122:        p->ptr = setbusy(allocp);
        !           123:        return((char *)(p+1));
        !           124: }
        !           125: 
        !           126: /*
        !           127:  *     freeing strategy tuned for LIFO allocation
        !           128:  */
        !           129: 
        !           130: free(ap)
        !           131: 
        !           132:        register char *ap;
        !           133: {
        !           134:        register union store *p = (union store *)ap;
        !           135: 
        !           136:        ASSERT(p != 0,(long));
        !           137:        ASSERT(p>clearbusy(allocs[1].ptr)&&p<=alloct,(long));
        !           138:        ASSERT(allock(),(long));
        !           139:        allocp = --p;
        !           140:        ASSERT(testbusy(p->ptr),(long));
        !           141:        p->ptr = clearbusy(p->ptr);
        !           142:        ASSERT(p->ptr > allocp && p->ptr <= alloct,(long));
        !           143:        return(NULL);
        !           144: }
        !           145: 
        !           146: #ifdef debug
        !           147: allock()
        !           148: {
        !           149: #ifdef longdebug
        !           150:        register union store *p;
        !           151:        int x;
        !           152:        x = 0;
        !           153:        for(p= &allocs[0]; clearbusy(p->ptr) > p; p=clearbusy(p->ptr)) {
        !           154:                if(p==allocp)
        !           155:                        x++;
        !           156:        }
        !           157:        ASSERT(p==alloct,(long));
        !           158:        return(x==1|p==allocp);
        !           159: #else
        !           160:        return(1);
        !           161: #endif
        !           162: }
        !           163: #endif

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